With the advance of biotechnology, enzymes or enzyme-producing cells are often used for industry and other fields in immobilized form, for it is easy to separate and recover them from products for repeated usage, and they are more stable than free enzymes. There are many immobilization methods such as physical absorption, affinity linkage, covalent crosslinking, flocculation and encapsulation.
The level of the immobilization technology is usually assessed by the specific activity (the activity of unit weight of immobilized enzyme/immobilized cell). The specific activity is related to the immobilization method and to the surface area (specific surface area) of the unit weight of immobilized enzymes/cells. Generally, the larger the specific surface area is, the higher the specific activity is. Many immobilization methods therefore rely on the increase of the specific surface area of the enzyme particle. At present, the common methods for increasing the specific surface area include using porous and small sized carrier, and applying small particulate carriers having prefabricated capillary pores to adsorb or hold cells and enzymes.
However, the present technology is greatly restricted in increasing the specific surface area of immobilized enzymes/cells. The existing organic or inorganic carriers are mostly made from hard materials with the pores generally present on the surface of the carriers, for the carriers will easily be cracked if there are too many internal pores. Consequently, the scientists of the field are searching for immobilized carriers with large specific surface area and less prone to break.